14 April 2011

Not looking for tail, revisited

In today’s “Science is incremental” department...

A couple of of years ago, I wrote about a paper with the counterintuitive finding that peahens do not prefer peacocks with large tails. At the time, I bemoaned that the authors hadn’t done an experiment. They hadn’t manipulated anything, and were dealing with a trait that varied little across males they were studying.

I am pleased to report that Dakin and Montgomerie have done an experiment. There’s a lot going on in this paper, but the critical one for me was that they measured, then changed, the number of visible “eyespots” in the peacock’s tail. The males whose eyespots had been removed had fewer copulations than those that were intact.

That said, the number of eyespots and the length of the tailfeathers in the intact animals didn’t correlate well with mating success.

The females, then, are paying attention to the tails... but the deviation has to be fairly large before they care. The experimental removal of eyespots put the peacocks in the bottom 10% of the range that has been reported for wild peacocks. I’m still waiting for someone to figure out how to add feathers on to a peacock to see if that would make a super successful male.

Peahens are not mating randomly, though, so what they use to assess a “high quality male” once you get past a certain threshold for the size of tail is not clear.